A large proportion of industrial injuries result from manual materials handling tasks. Back injuries occur with great frequency, often cause acute suffering and serious disability in the workers involved, and are extremely costly to the industrial economy. The objectives of this research are (1) to analyze the three- dimensional force systems that act in the human spine during industrial handling and lifting tasks, (2) to analyze the mechanical stresses within the intervertebral motion segments caused by these systems, and on the basis of this information, (3) to recommend methods for handling and lifting, and limitations on loads so that excessive stress levels in the spine can be avoided. A basic feature of the program is the use of computer-generated analogs of the thoracolumbar spine and finite-element models of single intervertebral motion segments for the study of the biomechanics of manual materials handling. The results of these studies may lead to significant breakthroughs in learning how the incidence and severity of industrial back injuries can be reduced.